Hitherto, in general, a coated tool is known, in which a hard coating layer is vapor-deposited on the surface of a body (hereinafter, collectively referred to as a tool body) made of tungsten carbide (hereinafter, referred to as WC)-based cemented carbide or titanium carbonitride (hereinafter, referred to as TiCN)-based cermet, the hard coating layer including:
(a) as a lower layer, a Ti compound layer composed of one or more of a Ti carbide (hereinafter, referred to as TiC) layer, a Ti nitride (hereinafter, similarly referred to as TiN) layer, a Ti carbonitride (hereinafter, referred to as TiCN) layer, a Ti oxycarbide (hereinafter, referred to as TiCO) layer, and a Ti oxycarbonitride (hereinafter, referred to as TiCNO) layer; and
(b) as an upper layer, an aluminum oxide layer (hereinafter, referred to as an Al2O3 layer) having an α-crystal structure in a chemically vapor-deposited state.
The conventional coated tool exhibits excellent wear resistance, for example, during continuous cutting or intermittent cutting of various types of steels or cast iron. However, in a case where the coated tool is used for high-speed intermittent cutting, there is a problem in that peeling or chipping of the coating layer easily occurs and the service life of the tool is reduced.
In order to suppress peeling or chipping of the coating layer, various coated tools with improved upper layers have been proposed.
For example, in Japanese Unexamined Patent Application, First Publication No. 2006-289557, a coated tool is proposed, in which a hard coating layer is vapor-deposited on the surface of a tool body, the hard coating layer including:
(a) as a lower layer, a Ti compound layer composed of one or more of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer, and having an average total layer thickness of 3 to 20 μm; and
(b) as an upper layer, a modified Al—Zr complex oxide layer having an average layer thickness of 1 to 15 μm and an α-crystal structure in a chemically vapor-deposited state, satisfying a composition formula of (Al1-XZrX)2O3 (X:0.003 to 0.05 in terms of atomic ratio), and having properties indicated by a constituent atom-sharing lattice point distribution graph in which the highest peak exists at Σ3 and the distribution ratio of Σ3 to the entire ΣN+1 is 60 to 80%. The constituent atom-sharing lattice point distribution graph is obtained by utilizing a field-emission-type scanning electron microscope, irradiating electron beams to individual crystal grains with a hexagonal crystal lattice in a measurement range of a polished surface, measuring an inclination angle between the normal line to the polished surface and the normal lines to a (0001) plane and a (10-10) plane as a crystal planes of the crystal grains which have a corundum hexagonal close-packed crystal structure in which constituent atoms composed of Al, Zr, and oxygen are present at each of the lattice points, and calculating a distribution of lattice points (constituent atom-sharing lattice points) where each constituent atom shares one constituent atom interface between the adjacent crystal grains based on the resulting measured inclination angles; and the graph shows the distribution ratio of individual ΣN+1 to the entire ΣN+1, ΣN+1 representing a constituent atom-sharing lattice point type in which there are N lattice points sharing no constituent atoms between the constituent atom-sharing lattice points (here, N is an even number of 2 or higher in a crystal structure of a corundum-type hexagonal close-packing crystal, and, 4, 8, 14, 24, and 26 do not exist from the view point of a distribution frequency in a case where the upper limit of N is 28).
It is known that chipping resistance is improved by the coated tool during high-speed intermittent cutting work.
In addition, for example, in Japanese Unexamined Patent Application, First Publication No. 2010-110833, a surface-coated cutting tool is proposed, in which a hard coating layer is vapor-deposited on the surface of a tool body, the hard coating layer including:
(a) as a lower layer, a Ti compound layer composed of one or more of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer, and having an average total layer thickness of 3 μm to 20 μm;
(b) as an intermediate layer, an Al2O3 layer having an average layer thickness of 1 to 5 μm and having an α-crystal structure in a chemically vapor-deposited state; and
(c) as an upper layer, a Zr-containing Al2O3 layer having an average layer thickness of 2 to 15 μm and having an α-crystal structure in a chemically vapor-deposited state.
In this tool, the intermediate layer (b) has properties indicated by an inclination angle frequency distribution graph in which the highest peak exists in an inclination angle division ranging 0 to 10° and the total sum of frequencies in the range of 0 to 10° occupies a ratio of 45% or more of the total frequencies in the inclination angle frequency distribution graph, the inclination angle frequency distribution graph being obtained by utilizing a field-emission-type scanning electron microscope, irradiating electron beams to individual crystal grains with a hexagonal crystal lattice in a measurement range of a polished surface of the tool body, measuring an inclination angle between the normal line to the polished surface and the normal line to (0001) plane as a crystal plane of the crystal grains, dividing the measured inclination angles belonging to a range of 0 to 45° every pitch of 0.25°, and counting the frequencies in each division;
the upper layer (c) has properties indicated by an inclination angle frequency distribution graph in which the highest peak exists in an inclination angle division in the range of 0 to 10° and the sum of frequencies in the range of 0 to 10° occupies a ratio of 60% or more of the total frequencies in the inclination angle frequency distribution graph, the inclination angle frequency distribution graph being obtained by utilizing a field-emission-type scanning electron microscope, irradiating electron beams to individual crystal grains with a hexagonal crystal lattice in a measurement range of a polished surface of the tool body, measuring an inclination angle between the normal line to the polished surface and the normal line to (0001) plane as a crystal plane of the crystal grains, dividing the measured inclination angles belonging to a range of 0 to 45° every pitch of 0.25°, and counting the frequencies in each division;
the upper layer (c) is a Zr-containing Al2O3 layer, in which the insides of the crystal grains, which constitutes the upper layer (c) and occupies 60% or more as an area ratio in the crystal grains of the upper layer, are divided by at least one crystal lattice interface with the constituent atom-sharing lattice point type expressed by Σ3, when electron beams are irradiated to the individual crystal grains in a measurement range of a polished surface of the tool body by utilizing a field-emission-type scanning electron microscope and an electron backscatter diffraction-imaging device to measure angles between normal lines of crystal lattice faces with hexagonal crystal lattices and the normal line to the surface of the tool body, a crystal orientation relationship between the adjacent crystal lattices is calculated based on the measurement result, and a distribution of lattice points (constituent atom-sharing lattice points) where each constituent atom of a crystal lattice interface shares one constituent atom between the crystal lattices is calculated, and when ΣN+1 represents a constituent atom-sharing lattice point type in which there are N lattice points sharing no constituent atoms between the constituent atom-sharing lattice points (here, N is an even number of 2 or higher in a crystal structure of a corundum-type hexagonal close-packing crystal, and N does not include 4, 8, 14, 24, and 26 when the upper limit of N is set to 28 in view of distribution frequency); and
the Zr-containing Al2O3 layer has a structure made of crystal grains with a flat polygonal shape within a plane perpendicular to a layer thickness direction thereof when the structure of the upper layer (c) is observed by the field-emission-type scanning electron microscope.
It is known that chipping resistance is improved by the coated tool during high-speed intermittent cutting work.